In typical domestic refrigerators, a fresh food compartment and frozen food compartment separated from each other by a divider wall are cooled by a common compressor-condenser-evaporator system. The frozen food compartment is chilled to sub-freezing temperatures by a fan forcing air past the evaporator in the compartment. The fresh food compartment in turn is cooled by chilled freezer compartment air passing through a baffle in the divider wall.
Commonly, the temperature of the frozen food compartment is controlled directly by thermostat or microprocessor based cycling of the compressor to bring the frozen food compartment to its temperature set point. The temperature of the fresh food compartment in turn is controlled indirectly by operating the baffle to pass chilled frozen food compartment air through the divider wall into the fresh food compartment. When either compartment requires cooling, the evaporator fan is operated. During defrost, a defrost heater associated with the evaporator is energized and the baffle is closed.
Prior art controls require a baffle that is solenoid or bellows operated and further require relays or triacs to operate the compressor, fan and defrost heater. These controls accordingly are relatively complex, expensive and prone to failure. Furthermore, the continuous energization of relays or triacs whenever a load is energized adds undesirable heat to the compartment in which the devices are located. This heat must be removed by the refrigeration system requiring yet an additional expenditure of energy.
In copending application Ser. No. 870,328, supra, temperature control in multiple compartment refrigerators is simplified and made more reliable by a unitary electric switch and baffle control assembly comprising a cam mechanism that is linked to the baffle and has a profiled control surface adjacent a number of circumferentially arranged electric switches for operating the compressor, evaporator fan and defrost heater. As the cam is rotated bidirectionally by an electric motor to predetermined angles of rotation in response to output compounds from a microprocessor, the baffle is opened or closed and the switches are operated to cool the two compartments to their desired temperatures or to defrost the frozen food compartment. Particular cam angles of rotation corresponding to desired operating modes of the refrigerator are determined by fixed control resistors selected by the microprocessor in accordance with a demand for cooling or a defrost. The angle of rotation of the cam is measured by a potentiometer and is fed back to the control unit for comparison with the particular control resistor selected by the microprocessor.
This system, although satisfactory, requires a relatively expensive reversible electric motor to drive the cam bidirectionally, and the potentiometer for monitoring the angle of rotation of the cam must be a high quality, relatively expensive, potentiometer to provide an adequate component lifetime. However, virtually all potentiometers wear with frequent use over a long period of time and therefore will tend to become a source of component failure in the refrigerator. A need exists to reduce the cost and improve the reliability of a unitary electric switch and baffle control assembly of a type described in copending application Ser. No. 870,328.